A jo is a stick, generally made of Japanese white or red oak, about 120 cm in length.  It should be the height of the floor to your armpit.

Jodo is "the way of the staff", a modernized form of stick combat, based upon Shinto Muso-ryu jojutsu a Japanese art dating back almost 400 years.  The use of the staff in the present fashion is attributed to a master swordsman, Gonnosuke Katsukichi, in the early 1600s.  There were, however, wooden staff arts before his time.  The rokushaku bo (six-foot staff) was, for instance, used  a number of schools.  A tessenbo was used by warriors centuries before the jo came into existence.   A tessenbo is a hard wooden staff of a taped length and a hexagonal cross-section that has been reinforced with iron.

Of course, historically, the jo focused on the opponent being a swordsman and many of the methods of jodo are formulated on this premise.  The jo is not so much a practical weapon in modern times  - not as practical as the smaller siblings of hanbo and tanbo.  Nevertheless, there are some important lessons to be learned from practicing with the jo.  With its focus on self defence and combat, TJR focuses on these imperatives rather than the focus that koryu forms might apply.